Radioactive dating is an incredibly accurate means of dating the age of earth. This is because the radioactive isotopes present have an exact half-life that does not change. Hence, by measuring the content of the radioactive isotopes, you can easily tell when the radioactive pieces were full and hence tell the exact age of the specimen.
Geologists have used radioactive dating to date mummies as well as fossils and even specimens of land in order to discover the age of the specimen. The accurate half-lives of these isotopes leaves little space for error making radioactive dating an extremely popular means of telling the age of a sample.